What does placeholder mean in manhwas??

It's so the bot won't upload the same chapter as the placeholder and messing up the chapters

Bots steals chapters from other sites so the chapters might be messed up / bad fan translation etc.

And most manhwa's with placeholder is official update

Placeholders are there until the real chapter comes up. Kinda like when people reserve a seat or a table by placing their bag. The bag is the placeholder.

Uploaders usually do this so that mangago/other uploaders don't upload from the source they want/when they want.